Spark plug



Oct. 19, 1937. H. RABEZZANA SPARK PLUG Filed Jan. :50, 1937 3mm .Wscz o l /Pa bazzazza Patented Oct. 19, 1937 UNITED STATES SPARK PLUG Hector Rabezzana, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 30, 1937, Serial No. 123,160

Claims.

My invention relates to spark plugs for internal combustion engines and the object thereof is to provide plug features whereby a better heat conducting path than heretofore is provided from 5 the spark gap and inner end of the central insulated electrode to the shell or casing of the plug, and to the engine cylinder and the surrounding atmosphere; whereby the plug when in operation is maintained at a lower temperature than has heretofore commonly been the case.

The grounded electrode of a spark plug is carried by the shell or casing thereof, which is screwed into an- )ening in the cylinder wall; and such heat as it derives from the burning l5 gases flows with little or no resistance to the cylinder so that no difliculty is met with as regards inordinate heating of the shell electrode. The central electrode, however, is necessarily insulated from the shell and inasmuch as the insulating material used is an indifferent conductor of heat it follows that the central electrode structure, that is the central electrode itself, the insulating material used and the means for supporting the electrode structure within the shell,

tends to attain a temperature much higher than that of the shell electrode; which high temperature is inJurious to the inner end of the central electrode at the spark gap and to the insulating material adjacent thereto; which parts are exposed to the heating action of the burning gases within the engine cylinder. Furthermore these parts, being exposed to the high temperature of the burning gases, are likely to become heated to a temperature high enough to cause preignition and backilring of the combustible mixture,

which is objectionable in internal combustion engine operation.

The object of my invention therefore is to secure a more rapid dissipation of heat from the inner end of the central electrode and from the insulating material adjacent thereto, to the shell or casing of the plug and to the surrounding atmosphere, by providing a better heat conducting path from said parts to the shell (which is in good heat conducting relation to the cylinder of the engine) than has heretofore commonly been the case in spark plugs. The greater part of the heat naturally flows to the cylinder; but a lesser part is dissipated to the atmosphere by way of the exposed outer end of the shell and by radio shielding means carried by said outer end, when my invention is applied to a plug having radio shielding parts or features.

'nie embodiment of my invention illustrated includes certain features of the central electrode,

of this specification illustrate the preferred form that is a tubular copper sheath surrounding the same whereby a better heat conducting path along the electrode itself is provided; but this present invention is concerned with a tubular gland nut which supports the central electrode and the insulation therefor within the shell, and with the relation of the gland nut to the shell or casing; and not to particular features of the central electrode itself even though it has features which cooperate with gland nut features to maintain a lower temperature of the spark plug.

My invention is adapted for use in spark plugs having radio shielding features as well also as in spark plugs wherein radio shielding features are not present, and it is disclosed in connection with both such types of spark plugs. Furthermore and as certain features provided particularly for radio shielding cooperate with the shell to secure better cooling of the central electrode structure, I regard my invention in its more comprehensive embodiment as including certain features concerned particularly with radio'shielding, and so claim it in the more specific claims herewith presented.

The drawing accompanying and forming a part of my invention. My invention, however, is regarded as extending to and including such variations and modifications of the particular form thereof illustrated and hereinafter described as come within the scope of the concluding claims, wherein the particular features wherein my in-- vention consists are particularly pointed out.

In the drawing:

Figure 1 is a view showing a section upon a plane extending longitudinally thereof, of a radio shielded spark plug wherein my invention is present.

Figure 2 is a similar sectional view showing a spark plug made in accordance with my invention, but wherein radio shielding elements are not present.

Figure 3 is a view showing a section upon a transverse plane indicated by the line 33, Fig- 45 ure 1.

Referring now to the drawing, the numeral 9 designates the hollow shell or casing of a spark plug, the inner part II) thereof being threaded to screw into the usual spark plug opening in an 50 internal combustion engine cylinder, as shown; and H is the grounded or shell electrode shown as an annular member made of heat resisting metal, and which is welded to the extremity of the threaded part of the shell. Figure 1 shows a tubular shield l2 made of metal, and having a mica or equivalent material lining member it; likewise of tubular form, the metallic tube being for radio shielding purposes as is usual in shielded spark plugs; whereas in Figure 2 the shell, while it extends above the cylinder wall or head as is usual in spark plugs, is not provided with a metallic shield like the tube i2 for radio shielding.

The numeral it designates the central electrode of the plug, the same being commonly made from a metal somewhat deficient in heat conducting properties but having a copper sheath it; to increase its heat conductivity, whereby heat flows from the spark gap between its inner end and the shell electrode i l more readily than would otherwise be the case.

The numeral it designates a gland nut which carries the central electrode iii and forms apart of a central electrode structure which is removable as a unit from the shell it, and replaceable therein, to which end it is externally threaded at ii and screws into the outer end ofa passage extending through the shell; and is provided with a wrench receiving head i8 at its upper end of approximately the same diameter as its threaded part. This head is provided with recesses it for receiving prongs of a wrench; and the fact that the head is of the same diameter as the threaded part it permits the gland nut to be assembled within and removed from a shielding tube 8243 of less diameter than would be the case if the head was of the usual hexagonal form to receive a socket wrench.

Said central electrode structure includes also '(in the embodiment of my invention illustrated) an insulating member 20 made commonly of thin sheet mica rolled to form a tube, insulating members 2 i, 22 preferably in the form of assemblages of mica washers abutting against the outer and inner ends of the gland nut 86 and surrounding the ends of the tubular insulating member 20, and a tubular sleeve 23 which is forced into an annular chamber between the outer end of the gland nut and the tubular insulating member Ell to provide a gas-tight joint during the assembling of the parts to provide the central electrode structure which, as will be appreciated, may be removed as a unit from' the shell and replaced therein without changing the concentric relation between the lower end of the central electrode and the shell electrode H. A gasket 2% is commonly placed between a shoulder of the gland nut and a ledge 25 inside the shell or casing as shown.

The gland nut I6 is provided with a tubular extension 26 which extends from its threaded outer end into and fits closely within the inner threaded part it] of the shell or casing, and is in good heat conducting relation with the inner wall of the passage in the shell along which it extends as by making the inner end 21 of said part or extension of such diameter that it forms a close fit with said passage whereby direct metal to metal contact is secured between said extension and the interior of the passage along which it extends. The inner end of the central electrode 14 has an enlarged head 28, which is a common feature in spark plugs and between which and the inner end of the tubular extension 26 the inner insulating member 22 is held. as shown. The upper end of the insulating member 22 abuts against the inner end of the extension which, being in good heat conducting relation with the shell of the plug as explained, it follows that an unusually short and good heat conducting path is provided from the inner end of the central electrode and the inaoaaiee smating member 22 to the shell or casing of the plug and to the cylinder of the engine. Furthermore and because the ledge at 25 whereby the gasket as is supported is located above and beyond the inner threaded part iii of the shell, and above and beyond the upper surface of the cylinder wall into which the plug is screwed, it follows that a heat flow path of large section and of good heat conductivity, as indicated at 29, is provided between the inner threaded and the outer exposed parts of the shell; whereby heat flow from the threaded inner part to the exposed outer part of the shell and to the surrounding atmosphere is facilitated.

In view of the premises it will be appreciated that in my improved spark plug heat from the inner end 28 of the central electrode and from the inner insulating member 22 (which parts hecome highly heated when the engine is in operation) flows to the shell or casing of the plug through short heat conducting paths of good heat conductivity; part of the heat flowing directly to the shell by way of the extension 26 of the gland nut it, and another part thereof flowing along the central electrode and through the insulating tube 29 (mica being a fair conductor of heat) to the gland nut and to the shell. These paths of heat flow transfer a considerable amount of heat to the outer exposed end of the shell or casing of the plug from which it is dissipated to the surrounding atmosphere through the metallic tube l2 if the plug is of the type illustrated in Figure 1 having features for accomplishing radio shielding, or from said exposed end directly to the surrounding atmosphere if, as in the type of spark plug illustrated in Figure 2, no radio shielding means is present.

Having thus described and explained my invention I claim and desire to secure by Letters Patent:

1. In a spark plug and in combination with a shell or casing having a passage extending longitudinally thereof and the outer part 'of which passage is internally threaded to receive a gland nut, and the inner end of which shell is externally threaded; a gland nut the outer end of which is externally threaded to engage said internally threaded part, and which gland nut has an extension which extends into the threaded inner end of said shell and is in direct metal to metal contact with the interior of the passage in said inner end along which it extends; a central electrode extending through a passage in said gland nut; means for insulating said electrode from said gland nut, said means including an inner insulating member the upper end of which is in direct contact with the inner extremity of said extension; and a grounded electrode carried by the inner end of saidshell and arranged adjacent the inner extremity of said central electrode.

2. In a spark plug and in combination with a shell or casing having a passage extending longitudinally thereof and the outer part of which passage is internally threaded to receive a gland nut, and the inner end of which shell is externally threaded; a gland nut externally threaded at its outer end to engage said internally threaded part, and the inner end of which extends into the threaded inner end of said shell and is in direct metalto metal contact with the interior of the passage in the inner end of the shell along which it extends; a central electrode extending through a passage in said gland nut; means for insulating said electrode from said gland nut, said means including an inner insulating member the upper end of which is in direct contact with the inner extremity of the extending inner end aforesaid of said gland nut; a tubular metallic shield carried by the upper end of said shell or casing; and a grounded electrode carried by the inner end of said shell and arranged adjacent the inner extremity oi said central electrode.

3. In a spark plug and in combination with a shell or casing having a passage extending longitudinally thereof and the outer part 01. which passage is internally threaded to receive a gland nut, and the inner end of which shell is externally threaded; a tubular metallic shield carried by the upper end of said shell or casing; a gland nut externally threaded at its outer end to engage said internally threaded part and having a wrench receiving portion which is of substantially the same diameter as said externally threaded outer end, and which gland nut has an extension extending into the part of the passage aforesaid which is within the threaded inner end of said shell and is in direct metal to metal contact with the interior of said passage; a central electrode extending through a passage in said gland nut; means for insulating said electrode from said gland nut, said means including an inner insulating member the upper end 01' which is in direct contact with the inner extremity of said extension; and a grounded electrode carried by the inner end of said shell and arranged adjacent the inner extremity of said central electrode.

4. In a spark plug and in combination with a shell or casing having an externally threaded inner part adapted to screw into an opening in an engine cylinder, an inner passage extending along said inner part.an internal shoulder located above the upper end of said inner passage, and an outer internally threaded passage of greater diameter than said inner passage extending from said internal shoulder to the outer end of said shell and adapted to receive a gland nut; a gland nut externally threaded at its outer end to engage with the threads within said outer passage and which gland nut is supported by said internal shoulder, and has an extension extending into said inner passage and which extension is in direct metal to metal contact with the interior 01 said passage; a central electrode extending through a passage in said gland nut; means for insulating said electrode from said gland nut, said means including an inner insulating member the upper end of which is in direct contact with the inner extremity of said extension; and a grounded electrode carried by the inner end of said shell and arranged adjacent the inner extremity of said central electrode.

5. In a spark plug and in combination with a shell or casing having an externally threaded inner part adapted to screw into an opening in an engine cylinder, an inner passage extending along said inner part, an internal shoulder located above the upper end of said inner passage, and an outer internally threaded passage of greater diameter than said inner passage extending from said internal shoulder to the outer endof said shell and adapted to receive a gland nut; a gland nut externally threaded at its outer end to engage with the threads within said outer passage and which gland nut is supported by said internal shoulder, and has an extension extending into said inner passage and which extension is in direct metal to metal contact with the interior of said passage; a central electrode extending through a passage in said gland nut; means for insulating said electrode from said gland nut, said means including an inner insulating member the upper end of which is in direct contact with the inner extremity of said extension; a tubular metallic sleeve carried by the upper end of said shell or casing; and a grounded electrode carried by the inner end 01 said shell and arranged adjacent the inner extremity of said central electrode.

HECTOR RABEZZANA. 

